This invention relates to electric cables, and methods of manufacturing and using such cables. In one aspect, the invention relates to electric cables with light weight corrosion resistant armor wires used with wellbore devices to analyze geologic formations adjacent a wellbore, methods of manufacturing same, as well as uses of such cables.
Generally, geologic formations within the earth that contain oil and/or petroleum gas have properties that may be linked with the ability of the formations to contain such products. For example, formations that contain oil or petroleum gas have higher electrical resistivity than those that contain water. Formations generally comprising sandstone or limestone may contain oil or petroleum gas. Formations generally comprising shale, which may also encapsulate oil-bearing formations, may have porosities much greater than that of sandstone or limestone, but, because the grain size of shale is very small, it may be very difficult to remove the oil or gas trapped therein. Accordingly, it may be desirable to measure various characteristics of the geologic formations adjacent to a well before completion to help in determining the location of an oil- and/or petroleum gas-bearing formation as well as the amount of oil and/or petroleum gas trapped within the formation. The zones to be analyzed can be vertically underneath the well bore surface opening or at angles deviated up to 90 degrees or more from the main well bore.
Logging tools, which are generally long, pipe-shaped devices may be lowered into the well to measure such characteristics at different depths along the well. These logging tools may include gamma-ray emitters/receivers, caliper devices, resistivity-measuring devices, neutron emitters/receivers, and the like, which are used to sense characteristics of the formations adjacent the well. A wireline cable connects the logging tool with one or more electrical power sources and data analysis equipment at the earth's surface, as well as providing structural support to the logging tools as they are lowered and raised through the well. Generally, the wireline cable is spooled out of a truck or an offshore platform unit, over a pulley, and down into the well.
Wireline cables are typically formed from a combination of metallic conductors, insulative materials, filler materials, jackets, and metallic armor wires. Armor wires typically perform many functions in wireline cables, including protecting the electrical core from the mechanical abuse seen in typical downhole environment, and providing mechanical strength to the cable to carry the load of the tool string and the cable itself.
Armor wire performance may also be dependent on corrosion protection. Harmful fluids in the downhole environment may cause armor wire corrosion, and once the armor wire begins to corrode, strength and pliability may be quickly compromised. Although the cable core may still remain functional, it is not economically feasible to replace the armor wire(s), and the entire cable must typically be discarded.
Conventionally, wellbore electrical cables utilize galvanized steel armor wires (typically plain carbon steels in the range AISI 1065 and 1085), known in the art as Galvanized Improved Plow Steel (GIPS) armor wires, which do provide high strength. Such armor wires are typically constructed of cold-drawn pearlitic steel coated with zinc for moderate corrosion protection. The GIPS armor wires are protected by a zinc hot-dip or electrolytic coating that acts as a sacrificial layer when the wires are exposed to moderate environments.
Commonly, sour well cables constructed completely of corrosion resistant alloys are used in sour well downhole conditions. While such alloys are well suited for forming armor wires used in cables for such wells, it is commonly known that the strength of such alloys is very limited.
As deviations in the well bores are increasing, the zones to be reached for evaluation or production may be at large angles relative to the well bore opening. To reach these zones, the cable must be tractored, but the reach may be limited as cables with galvanized steel armor wires may not be sufficiently light to satisfy these requirements. Furthermore, deviated well bores are typically sour as higher concentrations of corrosive agents are typically present.
Thus, a need exists for electric cables that are low weight with improved corrosion and abrasion protection. An electrical cable that can overcome one or more of the problems detailed above while conducting larger amounts of power with significant data signal transmission capability, would be highly desirable, and the need is met at least in part by the following invention.